Estimation of biological kinetic parameters from an analysis of the BOD curve of waste waters–effects of a chemical preoxidation

Abstract

Urban waste waters were treated with pure ozone or combinations of ozone. hydrogen peroxide and/or UV radiation to study the course of resulting BOD (biological oxygen demand)-time profiles and to propose a kinetic model. BOD-time profiles of chemically treated waste waters show an initial lag period that first order kinetic models cannot describe. A second order kinetic model is then proposed that satisfactorily fits experimental BOD-time profiles. except when hydrogen peroxide has been used. In these cases, BOD-time profiles present the highest lag periods observed. By applying this model, three parameters are determined: the biokinetic constant (k) which is an index of the biological removal rate; the potential amount of biodegradable matter (BOW), and the measure of the size of inocula and microbial activities of microorganisms (a). The model was checked with experimental results of BOD-time protiles corresponding to both untreated and chemically ozonated urban waste waters. Ozonated waste waters showed the highest values of k and B O R , which implies an improvement of waste water biodegradability after ozonation. However, values of d corresponding to ozonated waste waters presented lower values than those of untreated waste waters This was due to the lag period observed in the BOD-time profile. which was a consequence of a lack of microorganism acclimation to ozonated waste waters. The effect of the ozone dose, pH and carbonates during ozonation on COD (chemical oxygen demand) and the above indicated parameters was also studied. There was an optimum ozone dose which was 138 mg/l for this specific system. This led to the highest biodegradable fraction (q) and the highest biokinetic constant (39% increase in pand 4.7-fold increase in the value of k, respectively, compared to untreated waste waters.). Another significant fact was that a higher COD reduction w s observed in the absence of carbonate during ozonation at basic pH values. In addition, the percentage of variation in the biodegradable fraction (Ap) of ozonated waste water increased compared to the untreated waste water at acid pH. The results suggest that ozonolysis, the direct molecular ozone way of reaction, due to its selective character, increases the biodegradability of waste water more than other chemically advanced oxidation processes based on hydroxyl radical reactions.

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 2. Ozonation followed by biological oxidation

“…The variation of BOD with ozonation, observed in Table 1, implies an improvement of biodegradability measured as the ratio BOD/COD. 9 As can be observed from Fig 2, the highest value of this ratio corresponds to an optimum ozone consumed dose of approximately 40 g m À3 . ; C O3g = 2±15 g m À3 Subscript notation; i = initial (at the wastewater inlet); f = ®nal (at the wastewater outlet).…”

Integration of Advanced Oxidation Technologies and Biological Processes: Recent Developments, Trends, and Advances

“…[40] For the low level of ozone, the most oxidized compounds are removed by direct reaction. [44] At this point, ozonation is stopped to allow the biodegradable compounds, which were formed during the chemical step, to be degraded. [27] The reduction in COD removal is also decreased due to the reaction of ozone with biological compounds.…”

“…For ozone doses of more than its optimum, in addition to above, ozone starts to accumulate and decompose to yield free radicals, but they could not attack as they had been scavenged by bicarbonates. [44] Treatment Time The ozone concentration in the solution may rise to a point and ozone freezes at that point.…”

Integrated treatment of PAH contaminated soil by soil washing, ozonation and biological treatment

“…At higher ozone dozes, biodegradable compounds, both initially present and formed as a result of ozonation, compete for the available ozone [22,[29][30][31][32][33]. Therefore it is not always worthwhile to increase the ozone dose too much, and it is important to determine the optimum ozone dose so, that a higher fraction of dissolved matter can be eliminated, e.g.…”